These beings seem to be remarkable in some ways, as we are told by Muhammad al-Bukhari in his collection of HadithsSahih Bukhari:

...(who will be so beautiful, pure and transparent that) the marrow of the bones of their legs will be seen through[note 3] the bones and the flesh.[1]

They will not urinate, relieve nature, spit,[note 4] or have any nasal secretions. Their combs will be of gold, and their sweat will smell like musk. The aloes-wood will be used in their centres.[note 3] Their wives will be houris. All of them will look alike and will resemble their father Adam[note 5] (in statute), sixty cubits tall.[2][3]

All of which (especially the "sixty cubits" part, which would make them well over 100 feet tall, and a proportionally sized vagina about half a meter in diameter) may go some way to explaining their perpetual virginity. All in all, this scenario suspiciously resembles a teenage boy's fantasy, which may provide some insight into the intended target demographics of the original preachers.

The ghilman (ghulam in singular) are eternally youthful boys that serve both men and women in Paradise, and are often likened to waiters or eunuchs who serve their masters. Incidentally, the word "ghilman" was also the name for slave-soldiers in the Ottoman, Mughal and Persian empires.

↑There is an underlying assumption that devout Muslims are interested in houris and not, for example gay men, after all gay sex is forbidden in Islam. Both genders are covered, assuming they are straight and not asexual.